The present invention relates to a method and system for determining the state of charge and defining a charging algorithm for lithium ion (Li-ion) batteries and more particularly, to a method and system of determining and charging Li-ion batteries while the batteries remain floating on the direct current (DC) bus without the need for a dedicated charger.
Lithium Ion batteries integrated in an electrical power system need to be charged in a short time and in a way that guarantees their safe and optimal charging. Present methods include charging batteries via dedicated chargers, internal or external to the batteries and the battery envelope or external to the battery.
Li-Ion batteries are an emerging technology in the area of energy storage. Due to their particular chemistry and build, this emerging technology imposes more stringent methods of charging and discharging to ensure that operation safety margins are maintained. In addition, it is necessary to accurately determine the state of charge (SOC) of a Li-Ion battery in order to be aware of the reserves of stored energy in the system and to adapt the necessary measures as a result. When at a low SOC, the charging process must be re-started.
With respect to the charging process, a Li-Ion battery should not be charged beyond a certain limit. The charging current delivered to a Li-ion should be limited at the commencement of the start of charging and also when the battery approaches fully charge state. In addition, internal parameters of the battery, i.e., cell temperature, voltage, voltage balance between the different cells that constitute the battery, should be monitored and action taken if limits are exceeded.
As can be seen, there is a need for a system and method for accurately determining the SOC of a battery and safely charging the battery in an integrated power system.